DAIRY AND SEED IMPROVEMENT MEETINGS. 35 1 



Blackleg is a bacterial disease, is carried only by the seed 

 potatoes, and does not live over winter in the ground in Maine. 

 The next picture shows the base of an affected stem and a cross 

 section of a tuber having the characteristic soft rot or decay 

 associated with the disease. In this case the disease has spread 

 back from the parent stem along the tuber-bearing stolon and 

 affected the base of the young tuber. 



The next picture shows a potato plant grown in the green- 

 house and inoculated with a pure culture of the organism caus- 

 ing the disease. 



Blackleg is a comparatively easy disease to control. It may 

 be entirely eliminated by carefully sorting the seed and removing 

 all which show any rot or diseased areas or any which are appar- 

 ently cracked and jammed, and then disinfecting the remainder 

 wdth corrosive sublimate or formaldehyde before planting. Each 

 seed cutter should have two knives and a glass jar filled with 

 formaldehyde solution of the same strength as used for disin- 

 fecting the tubers. If, by chance, a diseased potato is overlooked 

 and found on cutting, it should be thrown away and the knife 

 dropped into the jar of disinfecting solution and the other used 

 in its place until another diseased potato is cut. 



COMMON AND POWDERY SCAB. 



The next picture shows a potato tuber attacked by common 

 scab. This condition is too well known and prevalent to require 

 comment. Potato scab has been reported on a few other vege- 

 tables or root crops, but on none of these is it of any importance 

 except occasionally on beets. The next picture shows a very 

 interesting case on turnips, the only one I have ever seen. 



There used to be much discussion and sometimes there is now 

 as to whether or not ashes, chip dirt, etc., could cause scab. It 

 was proven quite conclusively over twenty years ago, and has 

 been demonstrated repeatedly since, that the disease is of a para- 

 sitic nature and only can occur where the parasite exists in the 

 soil or is introduced with the seed tubers. The ashes, chip 

 dirt, etc., are favorable to the growth of the organism but do not 

 cause scab themselves. Regardless of how much lime or ashes 

 is placed in the soil, scab will not appear in experimental tests if 

 the soil is sterilized, and clean, disinfected tubers are planted 

 therein. 



